Diane K. Smith
Associate Professor
Analytical Chemistry
Office: CSL 412A
Office Phone: 619-594-4839
e-mail: dsmith_at_sciences.sdsu.edu
Research Interests
For good reason, chemistry is often called the “Molecular Science.” Chemists today truly are masters of molecules—with increasing ease we connect together atoms to form an infinite variety of molecules from the very simple to the extremely complex. However, beyond the realm of the single molecule our mastery rapidly diminishes. Biological systems contain many extremely complex molecules, but not one of these by itself makes life possible. What makes life possible is the interactions between molecules, and this is something that chemists are only beginning to learn how to control. This field, sometimes called “Supramolecular” chemistry, is one of the frontier areas of chemical research, and one that my research group is actively engaged in.
My specialty is electrochemistry, which deals with the process and result of the most basic of all chemical reactions, electron transfer. Specifically, I’m interested in learning how electron transfer can be used to control and characterize interactions between molecules. The research, although fundamental in nature, could lead to a number of possible applications, particularly in analytical chemistry, including new types of electrochemical sensors and separation systems.
At present the focus of our efforts is the design and characterization of “redox-dependent” receptors. A receptor or host is a molecule that selectively binds another molecule, termed substrate or guest, by a variety of intermolecular interactions, all of which are substantially weaker than a covalent bond. Redox-dependent means that the receptor can be (1) reversibly reduced and oxidized, and (2) reduction or oxidation changes the binding affinity of the receptor with a particular substrate. If the latter occurs, then the redox potential of the receptor will change in the presence of the substrate. We use this change in receptor redox potential to characterize the redox-dependence. It can also form the basis of an electrochemical sensor for substrates that are not in themselves electroactive.
When we first began this work very little had been done with redox-dependent receptors for organic compounds. In 1992 my students and I, along with another group, reported the first well-characterized example of a non-biological, redox-dependent receptor for neutral aromatics. Since that time we have discovered and investigated several other organic redox-dependent receptors, and, in the process, elucidated a number of the criteria necessary for redox-dependence.
One class of receptor that we are currently exploring are those that function through perturbation of hydrogen bonding interactions. This work is particularly intriguing because we see very strong and selective effects with very simple receptors. An example of some of the experimental data for these type of receptors is shown in the figure below.
While the emphasis is electrochemistry, the nature of the research gives students in my group the opportunity to gain experience in a variety of areas, including chemical synthesis, spectroscopy and computer modeling. In addition, students are exposed to the full range of modern electroanalytical techniques.
Cyclic voltammograms of 9,10-phenanthrenequinone (PQ) in methylene chloride by itself (a), and in the presence of N,N’-diphenylurea (b). The large positive shift in the presence of urea demonstrates that PQ is a redox-dependent receptor for ureas.
Selected Publications
- Bu JJ, Lilienthal ND, Woods JE, Nohrden CE, Hoang KT, Truong D, Smith DK "Electrochemically controlled hydrogen bonding. Nitrobenzenes as simple redox-dependent receptors for arylureas," J. Am. Chem. Soc. 127 6423-6429 (2005).
- Lilienthal ND, Alsafar H, Conerty J, Smith DK "Development of chemical sensors based on redox-dependent receptors: N,N '-dimethyldiazapyrenium-modified electrodes," Analytical Chemistry 75 3322-3328 (2003).
- Ge Y, Smith DK, "Development of Chemical Sensors Based on Redox-Dependent Receptors. Preparation and Characterization of Phenanthrenequinone-Modified Electrodes," Anal. Chem. 72, 1860 (2000).
- Ge Y, Miller L, Ouimet T, Smith DK "Electrochemically Controlled Hydrogen Bonding. o-Quinones as Simple Redox-Dependent Receptors for Arylureas," J. Org. Chem. 65, 1831 (2000).